1. Technical Field
One or more embodiments of the present invention relate to a contact and a method for manufacturing the contact. For example, one or more embodiments of the present invention relates to the contact that is incorporated into a housing and forms a connector, and the method for manufacturing the contact.
2. Background Art
Small connectors that are packaged to wiring substrates are used for connecting flexible printed substrates and the like. Metal plates with thickness of about 100 μm are mostly used for contacts to be used in such connectors.
As a method for manufacturing the contact is generally a method for punching a thin metal plate with a press. In the manufacturing method with a press, for example as shown in FIG. 1A, a thin metal plate 11 is placed on a die 12 for press, and a press die 14 is moved down from above the die 12. As shown in FIG. 1B, the metal plate 11 is shear-fractured by a punching hole 13 of the die 12 and the press die 14, and thus a contact 15 is manufactured. In the contact 15 that is punched by pressing, minute unevenness is generated on its punched surface. FIG. 2 illustrates a cut section (microphotograph) of the metal plate punched with the press. As shown in FIG. 2, a sagging surface D1 having a smooth round shape, a glossy shear plane D2 on which vertical lines are arranged, a fracture surface D3 on which as if a metal material is torn off, and a burred surface D4 on which burr occurs are formed on the cut section of the metal plate punched by pressing in this order from an upper surface side to a lower side. Particularly, the shear plane D2 has unevenness whose difference of elevation is the largest in FIG. 2, and protrudes the highest from this cut section. FIG. 2 is upside down with respect to FIG. 1 and FIGS. 3A-3D.
FIGS. 3A to 3D illustrate a mechanism where the cut section in FIG. 2 is generated on the metal plate. As shown in FIG. 3A, when the press die 14 moves down, a lower surface of the press die 14 touches the metal plate 11 so as to push down the metal plate 11. When the press die 14 pushes down the metal plate 11, as shown in FIG. 3B, sagging (D1) is generated on a cutting edge side surface of the press die 14 and a cutting edge side surface of the die 12 on the metal plate 11, respectively. Further, when the press die 14 moves down, the metal plate 11 receives a shear stress from the press die 14 and the die 12, and a shear plane (D2) is generated following the sagging (D1). When the press die 14 is further moves down, as shown in FIG. 3C, cracks 16 are generated on the metal plate 11 respectively, by an edge of the press die 14 and an edge of the die 12. At this time, the cutting edge side surface of the press die 14 and the cutting edge side surface of the die 12 become shear planes, and the cracks 16 become fracture surfaces (D3). Thereafter, as shown in FIG. 3D, the crack 16 on the side of the press die 14 and the crack 16 on the side of the die 12 are connected, so that the punching is completed. Therefore, the punching work is completed at a stage that the press die 14 enters about ⅔ of the metal plate 11. A suitable gap is necessary between the side surface of the press die 14 and the side surface of the punching hole 13 in order to connect the crack 16 on the side of the press die 14 and the crack 16 on the side of the die 12. This gap is called as a clearance, but a burr (D4) occurs at an end of the contact 15 due to the clearance.
When an operation is repeatedly performed for a long time, destruction such as sudden fracture occurs on the contact. This is called as fatigue fracture. The fatigue fracture is caused by some factors, but when a load is repeatedly applied to a plate material such as a contact, a maximum stress is generated on the surface of the plate material, and stress concentration on concave portions due to surface roughness is one of the main factors of the fatigue fracture.
When the contact is manufactured by the pressing work, this cut section becomes an outer peripheral surface of the contact. When a contact point of the contact is pressure-welded with an electrode section on a counterpart side, a spring section (elastically deformed section) of the contact is warped by the stress. Particularly, when a contact pressure is heightened, a bending moment applied to the spring section becomes large accordingly. For this reason, a large load is applied to the contact section and the spring section, but when the surfaces of the contact section and the spring section become cut sections at the time of the pressing work, stress concentration occurs on the unevenness or the like of the shear plane, and thus a number of repetitive fracture times of the contact is reduced.
Particularly, the contact is also miniaturized according to weight saving and shortening of a connector. For this reason, an unevenness dimension ratio of the maximum stress portion of the contact to a part cross-section becomes large, and thus the contact is easily fractured.
Patent Document 1: Japanese Unexamined Patent Publication No. 2010-86878